The Structured Query Language(SQL) is a language that enables you to create and operate on relational databases, which are sets of related information stored in tables. SQL has proved to be a standard language as it allows users to learn one set of commands and use it to create, retrieve, alter, and transfer information regardless of whether they are working on a PC, a work station, a mini, or a mainframe.
There are numerous versions of SQL. The original version was developed at IBMís San Jose Research Laboratory(now the Almanden Research Center). This language originally called Sequel, was implemented as part of the System R project in early 1970s. the Sequel language has evolved since then and its name has changed to SQL. In 1986, the American National Standards Institute(ANSI) published an SQL standard that was updated again in 1992.
SQL has clearly established itself as the standard relational database language. Letís see a brief presentation of SQL.
- SQL is nothing but a query language.
- It can do the query a database.
- SQL is efficient.
- SQL is easy to learn and use.
- It can define the structure of the data, modify data in the database and specify security constraints.
- IBM developed the original version of SQL originally called Sequel, as part of the System R Project in the early 1970s.
- The Sequel language has evolved since then, and itís name has changed to SQL.
- Now a days many products support the SQL language.
- The American National Standard Institute(ANSI) has accepted SQL as the standard access language for relational database management system.
- This language is non-procedural.
- SQL was introduced by IBM.
SQL statements are used for:
- Querying data.
- Inserting, updating, and deleting rows in database.
- Creating, replacing, altering and dropping objects.
- Guaranteeing database consistency and integrity.
Writing SQL statements:
- SQL statements are not case sensitive.
- SQL statements can be on one or more lines.
- Keywords can not be abbreviated or split across lines.
- Clauses are usually placed on separate lines.
- Tabs and indents are used to enhance redability.
Types of SQL
- Data Definition Language(DDL)
- Data Manipulation Language(DML)
- Data Query Language(DQL)
- Transaction Control Language(TCL)